Add snake_case filter

This is intended to be used by tripleo_metrics_qdr and
tripleo_collectd.
The filter will convert from THTCamelCase to ansible_snake_case

Change-Id: Iec74b239cbcebaeb6c5f5736e3696e013b697c76
Co-authored-by: Chris Sibbitt <csibbitt@redhat.com>

tripleo_ansible/ansible_plugins/filter/helpers.py

@@ -51,7 +51,8 @@ class FilterModule(object):
             'get_filtered_role_resources': self.get_filtered_role_resources,
             'get_node_capabilities': self.get_node_capabilities,
             'get_node_profile': self.get_node_profile,
-            'tht_abspath': self.tht_abspath
+            'tht_abspath': self.tht_abspath,
+            'snake_case': self.snake_case,
         }
 
     def subsort(self, dict_to_sort, attribute, null_value=0):
@@ -519,6 +520,20 @@ class FilterModule(object):
             return_list.append({k: v})
         return return_list
 
+    def snake_case(self, camel_case_string):
+        """Convert from THTCamelCase to ansible_snake_case
+        This filter will return a snake_case version of the input string.
+        >>> filter_snake_case('CephStorage')
+        'ceph_storage'
+        >>> filter_snake_case('HTTPWorker')
+        'http_worker'
+        >>> filter_snake_case('MetricsQDR')
+        'metrics_qdr'
+        """
+        camel_case_string = re.sub(r'(.)([A-Z][a-z]+)', r'\1_\2',
+                                   camel_case_string)
+        return re.sub(r'([a-z0-9])([A-Z])', r'\1_\2', camel_case_string).lower()
+
     @staticmethod
     def get_filtered_service_chain(resource_chains, role_chain_resources):
         """Returned filtered service chains.

tripleo_ansible/tests/plugins/filter/test_helpers.py

@@ -1144,6 +1144,19 @@ class TestHelperFilters(tests_base.TestCase):
         result = self.filters.dict_to_list(data=dict)
         self.assertEqual(result, expected_list)
 
+    def test_snake_case(self):
+        expected_string = "ceph_storage"
+        result = self.filters.snake_case("CephStorage")
+        self.assertEqual(result, expected_string)
+
+        expected_string = "http_worker"
+        result = self.filters.snake_case("HTTPWorker")
+        self.assertEqual(result, expected_string)
+
+        expected_string = "metrics_qdr"
+        result = self.filters.snake_case("MetricsQdr")
+        self.assertEqual(result, expected_string)
+
     def test_get_changed_async_task_names_empty(self):
         result = self.filters.get_changed_async_task_names(data=[])
         self.assertEqual(result, [])